Can I use "this" in a companion object?

Question

In a companion object, I want to have a field recording all the instances instantiated from the companion class (it is abstract), can I do that?

Especially, I thought this would reference to any instances of the subclass, but it won't compile when I use it in a companion object.

score 6 · Answer 1 · answered Nov 03 '12 at 10:39

You'd need to code it yourself, for instance (not thread safe):

abstract class C {
  // executed by all subclasses during construction
  C.registerInstance(this) 
}


object C {
  private val instances = ListBuffer[C]()
  def registerInstance(c: C) {
    instances += c
  }
}

score 4 · Accepted Answer · answered Nov 03 '12 at 08:12

4

this in an object (doesn't matter if it's a companion object or not) refers to the object. E.g.

scala> object A { def foo = 1; def bar = this.foo } 
defined module A

scala> A.bar
res0: Int = 1

answered Nov 03 '12 at 08:12

Alexey Romanov

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Can I use "this" in a companion object?

2 Answers2